The field is reduction of noise, vibration, and harshness (NVH) in an internal combustion engine. More specifically, the field covers reduction of gear noise and vibration in an opposed-piston engine.
Gear vibration and clash in an internal combustion engine lead to intense whining and/or sharp impulse noise which can cause extreme operator and passenger discomfort. Engine whine and rattle also add to the constant cacophony that makes proximity to transportation routes very unpleasant. Consequently, performance standards and environmental regulations relating to vehicles increasingly include NVH limits.
Whenever gears interface with each other, there is side contact between the respective gear teeth. These teeth side contacts are classified as overrunning side contacts or driving side contacts. Because of these contacts, there is usually a gap between the interfacing gear teeth. As the gears rotate, these gaps are closed when the teeth make new contacts, which can result in gear rattle. Backlash in the gear trains of opposed-piston engines during torque reversals will also produce gear rattle.
The gear train of an opposed-piston engine with dual crankshafts inherently experiences torque reversal events that produce clatter and vibration. In the case where a phase difference is provided between the crankshafts in order to differentiate port opening and closing times, the gear train is subjected to a torque reversal at least once every cycle of engine operation. Even without an inter-crankshaft phase difference, momentary inter-gear torque reversals result from idler bounce and/or gear/shaft rotational distortion. Torque reversals result in crank train rattle when gear backlash and powertrain gear teeth clearances are present.
U.S. Pat. No. 3,719,103 describes a multi-ply gear construction designed to be quiet-running. The gear construction includes a plastic center panel fastened between a pair of opposite metal side plates. Peripheral teeth are cut into a peripheral edge of the assembled gear. The plastic material yields to the cutting process, but the metal material does not. As a result, the central plastic segment of each tooth expands after the cutting operation such that the surfaces of the center segment are displaced outwardly of the corresponding side metal segments. With this multi-ply construction a gear is meshed with another gear in a manner eliminating backlash and preventing metal-to metal contact.
With respect to elimination of gear noise, the multi-ply gear construction described in the '103 patent is deficient in several respects. For example, by cutting gear teeth in a single fabrication step, the post-cutting expansion of the gear segments in the plastic center panel is imprecise and uneven, leading to a substantial variance in contact surface contours which allow a certain level of gear teeth side shifts with metal-to-metal contact noise. Further, the teeth are straight cut, which limits opportunities for suppressing gear lash. Finally, the multi-ply gear is mounted to a shaft by means of a mounting boss without any anti-turn mechanism to counteract rotational distortion between gear and shaft.
Consequently, opposed-piston engines need quiet-running gears constructed to prevent gear teeth side shifts caused by torque reversals, crankshaft phase differences, and idler bounce. It is further desirable to provide such gears with anti-turn provisions to reduce gear/shaft rotational impact.